Throughout human history, people have dreamt of machines and robots that can be self-repairing and self-sustaining. Recent advances in nanomaterials and bio-inspired materials have expanded our knowledge on how nature designs biological materials systems. Self-healing and self-repairing research began to appear in the literature, albeit at its infancy. Most of these concepts involve the use of hollow fibers or micro-capsules or other micro-containers of healing agents and catalysts/initiators buried in polymeric microcapsules. When activated, the healing agents and initiators/catalysts combine to achieve repair of the polymer. Corrosion inhibitors have been stored in this way and have shown effectiveness in laboratory tests in enhancing corrosion resistance. Stored monomers and polymerization initiators have also been shown to initiate cross-linking polymerization to achieve repair of minor damage in polymeric materials. But repairing sliding contacts in machine elements such as gears, bearings, pivots, joints, transmissions, engines, etc., where metals and alloy components in sliding contacts are wearing out has not been explored or attempted.
In the current art of self-healing and self-repairing, the process generally involves several steps, including: 1) detecting signals from damaged elements to activate release of repairing agents; 2) releasing of repairing agents (can be pro-active, such as adding measured amount of repairing agent, or passive, such as exposure to air oxidation to open up the micro-capsules); 3) providing a suitable environment in which repairing action can proceed without hindrance; and 4) when the desired level of repair is reached, terminating the process either when it reaches an equilibrium or through exhaustion of repairing agents. Unlike biological systems, however, there is no natural re-generative process to be used in machine systems.